Polymers comprising ethylene and at least one or more .alpha.-olefin and optionally one or more diolefin make up a large segment of polyolefin polymers and will be addressed for convenience as "ethylene-.alpha.-olefin-diolefin copolymers" herein. Such polymers range from crystalline polyethylene copolymers to largely amorphous elastomers, with a new area of semi-crystalline "plastomers" in between. In particular, ethylene-.alpha.-olefin-diolefin elastomers are a well established class of industrial polymers having a variety of uses associated with their elastomeric properties, their thermo-oxidative stability, their solubility in hydrocarbon oleaginous fluids, and their capability for modifying the properties of polyolefin blends. Included in this terminology are the commercially available EPM (ethylene-propylene monomer) and EPDM (ethylene-propylene-diene monomer) rubbery polymers, both being vulcanizable by cross-linking, the addition of the diolefin, also known as diene monomer, providing increased ease of both cross-linking and functionalization.
Commercially prepared ethylene-.alpha.-olefin-diolefin elastomers have been traditionally been made via Ziegler-Natta polymerization with homogenous catalyst systems largely based on vanadium or titanium. Newer metallocene catalyst compounds have received attention due to their ease of larger monomer incorporation and potential increases in polymerization activities. Although broadly described as suitable for polyolefin solution polymerization processes, metallocene catalysts have shown limitations in their molecular weight capabilities. Due to relatively fast termination (or chain transfer) reactions, such as the .beta.-hydride elimination reaction, metallocene catalysts tend to produce polymers and copolymers of low molecular weights at high temperatures (M.sub.n not more than about 50,000). This problem becomes more pronounced when the .alpha.-olefin comonomer content is relatively high (above 10 mol. %), which further depresses the molecular weight. In addition, the incorporation of diolefins at high conversions are important, for example in the efficient production of effectively curable EPDM rubbers.
Japanese Unexamined patent application publication 94-80683 describes unbridged monocyclopentadienyl Group 4-6 metal compounds said to provide benefits for polypropylene polymerization and exemplifies the production of atactic polypropylene with (cyclopentadienyl) (bistrimethylsilylamide) titanium dichloride activated with methylalumoxane at 40.degree. C. The catalyst is said to be an active catalyst for polyolefin polymerization at temperatures of from -100.degree. C. to 200.degree. C., desirably at -50.degree. C. to 100.degree. C. Synthesis of this catalyst is described here and in "Dialkylamido derivative of [(.eta..sup.5 --C.sub.5 Me.sub.5)TiCl.sub.3 ], [{(.eta..sup.5 --C.sub.5 Me.sub.5 TiCl.sub.2 }.sub.3 (.mu.--O) and [{(.eta..sup.5 --C.sub.5 Me.sub.5 TiCl}.sub.3 (.mu.--O)]: X-ray crystal structure of [(.eta..sup.5 --C.sub.5 Me.sub.5)Ti(NMe.sub.2).sub.3 ", Mart'n et al, Journal of Organometallic Chemistry, 467 (1994), 79-84.
Catalyst systems based on monocyclopentadienyl titanium compounds activated with alumoxane suitable for the preparation of ethylene-.delta.-olefin copolymers of high molecular weight and high .alpha.-olefin content are described in U.S. Pat. No. 5,264,405. This patent teaches that the cyclopentadienyl group should be fully substituted with methyl groups and bridged to an amido group having having an aliphatic or alicyclic hydrocarbyl ligand bonded through a 1.degree. or 2.degree. carbon. Copolymerization of ethylene with propylene in Example 45 with a bridged monocyclopentadienyl Group 4 metal catalyst compound at 80.degree. C. produced a copolymer with 20 wt.% ethylene having an M.sub.n of about 20,080. In Example 55 with the same catalyst as with Example 45, at a reaction temperature of 140.degree. C., an ethylene-propylene copolymer having a density of 0.863, indicative of an amorphous ethylene copolymer, exhibited an M.sub.n of about 46,500.
U.S. Pat. No. 5,321,106 describes a broad class of Group 4 or Lanthanide series metal compounds useful as addition polymerization catalysts for ethylenically unsaturated monomers where activated by a cationic oxidizer, the compounds comprising an anionic or non-anionic ligand system ("L"), one of several being --NR.sub.2 where R is a hydrocarbyl, silyl, germyl, or a substituted hydrocarbyl, silyl, germyl group of from 1 to 24 carbon, silicon, or germanium atoms. The preferred catalysts are monocyclopentadienyl compounds having a divalent substituted cyclopentadienyl group linked through a Y heteroatom ligand, inclusive of nitrogen hetroatoms, to the Group 4 or Lanthanide series metal. Polymerization example 2 illustrates a preferred catalyst used for copolymerization of ethylene and 1-octene at a temperature of 150.degree. C.
The most commercially interesting molecular weight for elastomeric ethylene-a-olefin-diolefin copolymers exceeds about 50,000 M.sub.n. Further, the incorporation of high levels of diolefins, beyond those commercially provided by traditional Ziegler catalysts, is highly desired for improved capabilities for crosslinking in vulcanizates and in graft functionalization with non-hydrocarbyl moieties for improved compatibilities and applications requiring greater affinity to non-hydrocarbyl chemical compounds. Additionally, the use of high temperature solution processes provide the potential for industrial benefits in ease of handling the amorphous elastomers since their solubility in the polymerization solvent increases and solution viscosity is accordingly decreased. A traditional bottleneck in the manufacture of elastomeric polymers at high temperatures is their resulting low molecular weight. Thus an ability to capitalize on inherent solution viscosity improvements at operating temperatures higher than about 80.degree. C. while retaining high molecular weight polymers with high comonomer content is important.